A two part type acrylic adhesive composition is usually composed of a combination of an acrylate ester monomer, a polymer, an organic peroxide, and a hardening accelerator and according to the difference in compositions and properties, the adhesive composition is generally classified into two kinds which are called as "the first generation acrylic adhesive (hereinafter, is referred to as FGA) and "the second generation acrylic adhesive (hereinafter, is referred to as SGA). In conventionally known FGA, a graft polymerization between an acrylate ester monomer and a polymer is not performed during the hardening step because of the composition thereof and hence is adhesive faculty thereof is generally insufficient. On the other hand, in recently developed SGA, it is said that a graft polymerization between an acrylate ester monomer and a polymer is performed during the hardening step and hence SGA is greatly excellent in properties such as adhesive strength, heat resistance, chemical resistance, etc.
The SGA is generally classified into the following two kinds according to the kinds of polymers used for the adhesives.
One type of the adhesives uses chlorosulfonated polyethylene as the polymer as shown in U.S. Pat. No. 3,890,407/'75 and has a mechanism that a radical is formed at the side chain of the polymer at hardening and the acrylate ester monomer is graft polymerized to the polymer radical. The adhesive of this type has excellent shearing strength and impact strength but, on the other hand, the adhesive has such disadvantages as some insufficiency in peeling strength, unbalance in adhesive property according to a material to be adhered, and showing corrosive property to metals, and hence the adhesive is yet unsatisfactory as a structural adhesive. As another type of the adhesives, SGA using a dienic elastomer such as nitrile rubber, etc., as the polymer is known as described in Japanese Patent Publication (Unexamined) No. 129,438/'76 and Japanese Patent Publication Nos. 2231/'80; 2236/'80; 17,041/3 80; and 21,076/'80 but the adhesive is insufficient in adhesive property and long storage stability.
Furthermore, it is described in U.S. Pat. No. 4,223,115/'80 that an adhesive composition having an excellent adhesive property is obtained by using a phosphorus-containing compound such as phosphoric acid and an organic derivative of phosphinic acid, phosphonic acid, or phosphoric acid in the range of about 0.1 to about 20 parts by weight of a polymerizable adhesive composition containing a polymer. However, such a phosphorus-containing compound has a disadvantage of delaying the adhesive speed for the polymerizable adhesive composition. Accordingly, it has been attempted to accelerate hardening of the polymerizable adhesive composition by adding a specific tertiary amine having a strong toxicity, such as N,N-dimethylaniline and N,N-dimethylaminomethyl-phenol to the adhesive composition in an amount of about 0.01 to about 10% by weight, preferably about 0.5% to about 5% by weight of the adhesive composition, but there are some problems in the adhesive composition on the storage stability and use.